1. Field of the Invention
This invention relates to filter presses for separating solids from liquid and, more particularly, this invention relates to a mechanism and method for shifting groups of plates on filter presses.
2. State of the Art
Filter presses are well known for separating solids from liquids, slurries, suspensions and like aqueous feed streams. For example, filter presses are often utilized to dewater sewage sludge and various mineral slurries.
A filter press generally includes a series, or stack, of parallel plates covered on both sides with filter cloths and shaped to permit drainage. For filtration, the plates are forced into abutting relationship with one another by a slide head pushed by an hydraulic ram; then an aqueous feed stream is fed under pressure into the enclosed spaces between the successive abutting plates. The pressure of the feed stream forces liquid through the filter cloths, leaving behind cakes of solids on the cloths. After a period of time, the feed is stopped and the press is opened to separate the plates in the stack one from another. Following that, the cakes of the accumulated dewatered solids are discharged from the filter cloths.
In view of the preceding description, it may be appreciated that the term "press" is somewhat of a misnomer because filtration is not accomplished by mechanical squeezing. Instead, the pressure which accomplishes filtration is provided by a slurry or sludge pump operating on the feed stream. Typical pumps provide pressures up to several hundred psi.
To open a filter press, the aforementioned slide head is retracted and then the plates in the stack are shifted relative to one another in order to expose both sides of each plate for the discharge and removal of filter cake. Heretofore, various plate shifting devices have been devised or suggested. For example, my U.S. Pat. No. 3,306,455 teaches a carriage which is reciprocatable along the frame of a filter press to selectively move the filter plates one by one from one end of the filter press to the opposite end. As another example, my U.S. Pat. No. 3,232,435 teaches an automatic mechanism to separate and shift filter plates, again one by one. As still another example, U.S. Pat. No. 3,270,887 teaches a plate-and-frame type of filter press wherein a rotatable shaft is employed to separate groups of plates and frames after a slide head is retracted.